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diff --git a/Documentation/doc-guide/sphinx.rst b/Documentation/doc-guide/sphinx.rst new file mode 100644 index 000000000..cd8ad7904 --- /dev/null +++ b/Documentation/doc-guide/sphinx.rst @@ -0,0 +1,530 @@ +.. _sphinxdoc: + +===================================== +Using Sphinx for kernel documentation +===================================== + +The Linux kernel uses `Sphinx`_ to generate pretty documentation from +`reStructuredText`_ files under ``Documentation``. To build the documentation in +HTML or PDF formats, use ``make htmldocs`` or ``make pdfdocs``. The generated +documentation is placed in ``Documentation/output``. + +.. _Sphinx: http://www.sphinx-doc.org/ +.. _reStructuredText: http://docutils.sourceforge.net/rst.html + +The reStructuredText files may contain directives to include structured +documentation comments, or kernel-doc comments, from source files. Usually these +are used to describe the functions and types and design of the code. The +kernel-doc comments have some special structure and formatting, but beyond that +they are also treated as reStructuredText. + +Finally, there are thousands of plain text documentation files scattered around +``Documentation``. Some of these will likely be converted to reStructuredText +over time, but the bulk of them will remain in plain text. + +.. _sphinx_install: + +Sphinx Install +============== + +The ReST markups currently used by the Documentation/ files are meant to be +built with ``Sphinx`` version 1.7 or higher. + +There's a script that checks for the Sphinx requirements. Please see +:ref:`sphinx-pre-install` for further details. + +Most distributions are shipped with Sphinx, but its toolchain is fragile, +and it is not uncommon that upgrading it or some other Python packages +on your machine would cause the documentation build to break. + +A way to avoid that is to use a different version than the one shipped +with your distributions. In order to do so, it is recommended to install +Sphinx inside a virtual environment, using ``virtualenv-3`` +or ``virtualenv``, depending on how your distribution packaged Python 3. + +.. note:: + + #) It is recommended to use the RTD theme for html output. Depending + on the Sphinx version, it should be installed separately, + with ``pip install sphinx_rtd_theme``. + +In summary, if you want to install Sphinx version 2.4.4, you should do:: + + $ virtualenv sphinx_2.4.4 + $ . sphinx_2.4.4/bin/activate + (sphinx_2.4.4) $ pip install -r Documentation/sphinx/requirements.txt + +After running ``. sphinx_2.4.4/bin/activate``, the prompt will change, +in order to indicate that you're using the new environment. If you +open a new shell, you need to rerun this command to enter again at +the virtual environment before building the documentation. + +Image output +------------ + +The kernel documentation build system contains an extension that +handles images on both GraphViz and SVG formats (see +:ref:`sphinx_kfigure`). + +For it to work, you need to install both GraphViz and ImageMagick +packages. If those packages are not installed, the build system will +still build the documentation, but won't include any images at the +output. + +PDF and LaTeX builds +-------------------- + +Such builds are currently supported only with Sphinx versions 2.4 and higher. + +For PDF and LaTeX output, you'll also need ``XeLaTeX`` version 3.14159265. + +Depending on the distribution, you may also need to install a series of +``texlive`` packages that provide the minimal set of functionalities +required for ``XeLaTeX`` to work. + +Math Expressions in HTML +------------------------ + +Some ReST pages contain math expressions. Due to the way Sphinx works, +those expressions are written using LaTeX notation. +There are two options for Sphinx to render math expressions in html output. +One is an extension called `imgmath`_ which converts math expressions into +images and embeds them in html pages. +The other is an extension called `mathjax`_ which delegates math rendering +to JavaScript capable web browsers. +The former was the only option for pre-6.1 kernel documentation and it +requires quite a few texlive packages including amsfonts and amsmath among +others. + +Since kernel release 6.1, html pages with math expressions can be built +without installing any texlive packages. See `Choice of Math Renderer`_ for +further info. + +.. _imgmath: https://www.sphinx-doc.org/en/master/usage/extensions/math.html#module-sphinx.ext.imgmath +.. _mathjax: https://www.sphinx-doc.org/en/master/usage/extensions/math.html#module-sphinx.ext.mathjax + +.. _sphinx-pre-install: + +Checking for Sphinx dependencies +-------------------------------- + +There's a script that automatically check for Sphinx dependencies. If it can +recognize your distribution, it will also give a hint about the install +command line options for your distro:: + + $ ./scripts/sphinx-pre-install + Checking if the needed tools for Fedora release 26 (Twenty Six) are available + Warning: better to also install "texlive-luatex85". + You should run: + + sudo dnf install -y texlive-luatex85 + /usr/bin/virtualenv sphinx_2.4.4 + . sphinx_2.4.4/bin/activate + pip install -r Documentation/sphinx/requirements.txt + + Can't build as 1 mandatory dependency is missing at ./scripts/sphinx-pre-install line 468. + +By default, it checks all the requirements for both html and PDF, including +the requirements for images, math expressions and LaTeX build, and assumes +that a virtual Python environment will be used. The ones needed for html +builds are assumed to be mandatory; the others to be optional. + +It supports two optional parameters: + +``--no-pdf`` + Disable checks for PDF; + +``--no-virtualenv`` + Use OS packaging for Sphinx instead of Python virtual environment. + + +Sphinx Build +============ + +The usual way to generate the documentation is to run ``make htmldocs`` or +``make pdfdocs``. There are also other formats available: see the documentation +section of ``make help``. The generated documentation is placed in +format-specific subdirectories under ``Documentation/output``. + +To generate documentation, Sphinx (``sphinx-build``) must obviously be +installed. For PDF output you'll also need ``XeLaTeX`` and ``convert(1)`` +from ImageMagick (https://www.imagemagick.org).\ [#ink]_ All of these are +widely available and packaged in distributions. + +To pass extra options to Sphinx, you can use the ``SPHINXOPTS`` make +variable. For example, use ``make SPHINXOPTS=-v htmldocs`` to get more verbose +output. + +It is also possible to pass an extra DOCS_CSS overlay file, in order to customize +the html layout, by using the ``DOCS_CSS`` make variable. + +By default, the "Alabaster" theme is used to build the HTML documentation; +this theme is bundled with Sphinx and need not be installed separately. +The Sphinx theme can be overridden by using the ``DOCS_THEME`` make variable. + +There is another make variable ``SPHINXDIRS``, which is useful when test +building a subset of documentation. For example, you can build documents +under ``Documentation/doc-guide`` by running +``make SPHINXDIRS=doc-guide htmldocs``. +The documentation section of ``make help`` will show you the list of +subdirectories you can specify. + +To remove the generated documentation, run ``make cleandocs``. + +.. [#ink] Having ``inkscape(1)`` from Inkscape (https://inkscape.org) + as well would improve the quality of images embedded in PDF + documents, especially for kernel releases 5.18 and later. + +Choice of Math Renderer +----------------------- + +Since kernel release 6.1, mathjax works as a fallback math renderer for +html output.\ [#sph1_8]_ + +Math renderer is chosen depending on available commands as shown below: + +.. table:: Math Renderer Choices for HTML + + ============= ================= ============ + Math renderer Required commands Image format + ============= ================= ============ + imgmath latex, dvipng PNG (raster) + mathjax + ============= ================= ============ + +The choice can be overridden by setting an environment variable +``SPHINX_IMGMATH`` as shown below: + +.. table:: Effect of Setting ``SPHINX_IMGMATH`` + + ====================== ======== + Setting Renderer + ====================== ======== + ``SPHINX_IMGMATH=yes`` imgmath + ``SPHINX_IMGMATH=no`` mathjax + ====================== ======== + +.. [#sph1_8] Fallback of math renderer requires Sphinx >=1.8. + + +Writing Documentation +===================== + +Adding new documentation can be as simple as: + +1. Add a new ``.rst`` file somewhere under ``Documentation``. +2. Refer to it from the Sphinx main `TOC tree`_ in ``Documentation/index.rst``. + +.. _TOC tree: http://www.sphinx-doc.org/en/stable/markup/toctree.html + +This is usually good enough for simple documentation (like the one you're +reading right now), but for larger documents it may be advisable to create a +subdirectory (or use an existing one). For example, the graphics subsystem +documentation is under ``Documentation/gpu``, split to several ``.rst`` files, +and has a separate ``index.rst`` (with a ``toctree`` of its own) referenced from +the main index. + +See the documentation for `Sphinx`_ and `reStructuredText`_ on what you can do +with them. In particular, the Sphinx `reStructuredText Primer`_ is a good place +to get started with reStructuredText. There are also some `Sphinx specific +markup constructs`_. + +.. _reStructuredText Primer: http://www.sphinx-doc.org/en/stable/rest.html +.. _Sphinx specific markup constructs: http://www.sphinx-doc.org/en/stable/markup/index.html + +Specific guidelines for the kernel documentation +------------------------------------------------ + +Here are some specific guidelines for the kernel documentation: + +* Please don't go overboard with reStructuredText markup. Keep it + simple. For the most part the documentation should be plain text with + just enough consistency in formatting that it can be converted to + other formats. + +* Please keep the formatting changes minimal when converting existing + documentation to reStructuredText. + +* Also update the content, not just the formatting, when converting + documentation. + +* Please stick to this order of heading adornments: + + 1. ``=`` with overline for document title:: + + ============== + Document title + ============== + + 2. ``=`` for chapters:: + + Chapters + ======== + + 3. ``-`` for sections:: + + Section + ------- + + 4. ``~`` for subsections:: + + Subsection + ~~~~~~~~~~ + + Although RST doesn't mandate a specific order ("Rather than imposing a fixed + number and order of section title adornment styles, the order enforced will be + the order as encountered."), having the higher levels the same overall makes + it easier to follow the documents. + +* For inserting fixed width text blocks (for code examples, use case + examples, etc.), use ``::`` for anything that doesn't really benefit + from syntax highlighting, especially short snippets. Use + ``.. code-block:: <language>`` for longer code blocks that benefit + from highlighting. For a short snippet of code embedded in the text, use \`\`. + + +the C domain +------------ + +The **Sphinx C Domain** (name c) is suited for documentation of C API. E.g. a +function prototype: + +.. code-block:: rst + + .. c:function:: int ioctl( int fd, int request ) + +The C domain of the kernel-doc has some additional features. E.g. you can +*rename* the reference name of a function with a common name like ``open`` or +``ioctl``: + +.. code-block:: rst + + .. c:function:: int ioctl( int fd, int request ) + :name: VIDIOC_LOG_STATUS + +The func-name (e.g. ioctl) remains in the output but the ref-name changed from +``ioctl`` to ``VIDIOC_LOG_STATUS``. The index entry for this function is also +changed to ``VIDIOC_LOG_STATUS``. + +Please note that there is no need to use ``c:func:`` to generate cross +references to function documentation. Due to some Sphinx extension magic, +the documentation build system will automatically turn a reference to +``function()`` into a cross reference if an index entry for the given +function name exists. If you see ``c:func:`` use in a kernel document, +please feel free to remove it. + +Tables +------ + +ReStructuredText provides several options for table syntax. Kernel style for +tables is to prefer *simple table* syntax or *grid table* syntax. See the +`reStructuredText user reference for table syntax`_ for more details. + +.. _reStructuredText user reference for table syntax: + https://docutils.sourceforge.io/docs/user/rst/quickref.html#tables + +list tables +~~~~~~~~~~~ + +The list-table formats can be useful for tables that are not easily laid +out in the usual Sphinx ASCII-art formats. These formats are nearly +impossible for readers of the plain-text documents to understand, though, +and should be avoided in the absence of a strong justification for their +use. + +The ``flat-table`` is a double-stage list similar to the ``list-table`` with +some additional features: + +* column-span: with the role ``cspan`` a cell can be extended through + additional columns + +* row-span: with the role ``rspan`` a cell can be extended through + additional rows + +* auto span rightmost cell of a table row over the missing cells on the right + side of that table-row. With Option ``:fill-cells:`` this behavior can + changed from *auto span* to *auto fill*, which automatically inserts (empty) + cells instead of spanning the last cell. + +options: + +* ``:header-rows:`` [int] count of header rows +* ``:stub-columns:`` [int] count of stub columns +* ``:widths:`` [[int] [int] ... ] widths of columns +* ``:fill-cells:`` instead of auto-spanning missing cells, insert missing cells + +roles: + +* ``:cspan:`` [int] additional columns (*morecols*) +* ``:rspan:`` [int] additional rows (*morerows*) + +The example below shows how to use this markup. The first level of the staged +list is the *table-row*. In the *table-row* there is only one markup allowed, +the list of the cells in this *table-row*. Exceptions are *comments* ( ``..`` ) +and *targets* (e.g. a ref to ``:ref:`last row <last row>``` / :ref:`last row +<last row>`). + +.. code-block:: rst + + .. flat-table:: table title + :widths: 2 1 1 3 + + * - head col 1 + - head col 2 + - head col 3 + - head col 4 + + * - row 1 + - field 1.1 + - field 1.2 with autospan + + * - row 2 + - field 2.1 + - :rspan:`1` :cspan:`1` field 2.2 - 3.3 + + * .. _`last row`: + + - row 3 + +Rendered as: + + .. flat-table:: table title + :widths: 2 1 1 3 + + * - head col 1 + - head col 2 + - head col 3 + - head col 4 + + * - row 1 + - field 1.1 + - field 1.2 with autospan + + * - row 2 + - field 2.1 + - :rspan:`1` :cspan:`1` field 2.2 - 3.3 + + * .. _`last row`: + + - row 3 + +Cross-referencing +----------------- + +Cross-referencing from one documentation page to another can be done simply by +writing the path to the document file, no special syntax required. The path can +be either absolute or relative. For absolute paths, start it with +"Documentation/". For example, to cross-reference to this page, all the +following are valid options, depending on the current document's directory (note +that the ``.rst`` extension is required):: + + See Documentation/doc-guide/sphinx.rst. This always works. + Take a look at sphinx.rst, which is at this same directory. + Read ../sphinx.rst, which is one directory above. + +If you want the link to have a different rendered text other than the document's +title, you need to use Sphinx's ``doc`` role. For example:: + + See :doc:`my custom link text for document sphinx <sphinx>`. + +For most use cases, the former is preferred, as it is cleaner and more suited +for people reading the source files. If you come across a ``:doc:`` usage that +isn't adding any value, please feel free to convert it to just the document +path. + +For information on cross-referencing to kernel-doc functions or types, see +Documentation/doc-guide/kernel-doc.rst. + +.. _sphinx_kfigure: + +Figures & Images +================ + +If you want to add an image, you should use the ``kernel-figure`` and +``kernel-image`` directives. E.g. to insert a figure with a scalable +image format, use SVG (:ref:`svg_image_example`):: + + .. kernel-figure:: svg_image.svg + :alt: simple SVG image + + SVG image example + +.. _svg_image_example: + +.. kernel-figure:: svg_image.svg + :alt: simple SVG image + + SVG image example + +The kernel figure (and image) directive supports **DOT** formatted files, see + +* DOT: http://graphviz.org/pdf/dotguide.pdf +* Graphviz: http://www.graphviz.org/content/dot-language + +A simple example (:ref:`hello_dot_file`):: + + .. kernel-figure:: hello.dot + :alt: hello world + + DOT's hello world example + +.. _hello_dot_file: + +.. kernel-figure:: hello.dot + :alt: hello world + + DOT's hello world example + +Embedded *render* markups (or languages) like Graphviz's **DOT** are provided by the +``kernel-render`` directives.:: + + .. kernel-render:: DOT + :alt: foobar digraph + :caption: Embedded **DOT** (Graphviz) code + + digraph foo { + "bar" -> "baz"; + } + +How this will be rendered depends on the installed tools. If Graphviz is +installed, you will see a vector image. If not, the raw markup is inserted as +*literal-block* (:ref:`hello_dot_render`). + +.. _hello_dot_render: + +.. kernel-render:: DOT + :alt: foobar digraph + :caption: Embedded **DOT** (Graphviz) code + + digraph foo { + "bar" -> "baz"; + } + +The *render* directive has all the options known from the *figure* directive, +plus option ``caption``. If ``caption`` has a value, a *figure* node is +inserted. If not, an *image* node is inserted. A ``caption`` is also needed, if +you want to refer to it (:ref:`hello_svg_render`). + +Embedded **SVG**:: + + .. kernel-render:: SVG + :caption: Embedded **SVG** markup + :alt: so-nw-arrow + + <?xml version="1.0" encoding="UTF-8"?> + <svg xmlns="http://www.w3.org/2000/svg" version="1.1" ...> + ... + </svg> + +.. _hello_svg_render: + +.. kernel-render:: SVG + :caption: Embedded **SVG** markup + :alt: so-nw-arrow + + <?xml version="1.0" encoding="UTF-8"?> + <svg xmlns="http://www.w3.org/2000/svg" + version="1.1" baseProfile="full" width="70px" height="40px" viewBox="0 0 700 400"> + <line x1="180" y1="370" x2="500" y2="50" stroke="black" stroke-width="15px"/> + <polygon points="585 0 525 25 585 50" transform="rotate(135 525 25)"/> + </svg> |